This invention relates to a oil-fill opening for introducing lubricating oil into a crankcase of an internal combustion engine comprising an oil-fill opening for introducing lubricating oil into a crankcase of an internal combustion engine, comprising a tubular oil-fill opening; a cap for opening and closing the oil-fill opening; an oil separator adjacent the oil-fill opening through which blow-by gases from the engine crankcase are conducted to the engine intake manifold or to the clean-air side of the engine air filter, and a return port communicating between the oil separator and the oil-fill opening for returning lubricating oil collected in the oil separator.
Such oil-fill openings are advantageously disposed on the valve chamber cover of the engine and generally comprise an oil-fill neck which is closed by a cap with a bayonet lock.
It is furthermore known to feed the blow-by gases which form in the crankcase through an oil separator to the engine intake manifold or to the clean-air side of the engine air filter. The oil collected in the oil separator is to be returned to the oil circuit. It has therefore proven desirable to dispose the oil separator, which separates the oil contained in the blow-by gas, directly adjacent the oil-fill opening and to create a connection between the oil separator and the oil-fill opening so that the separated oil can flow back into the valve chamber. It has been found, however, that when oil is poured into the oil-fill opening, especially when very large amounts of oil are poured in within a short period of time, there is a danger that this oil will get into the oil separator and, under certain circumstances, it may enter the line connecting the oil separator to the intake manifold. This results in the air filter cartridge being ruined by the inflowing oil.